U.S. patent number 6,254,954 [Application Number 09/367,958] was granted by the patent office on 2001-07-03 for pressure-sensitive adhesive tape.
This patent grant is currently assigned to 3M Innovative Properties Company. Invention is credited to Greggory S. Bennett, Clayton A. George, Guido Hitschmann, Alain H. Lamon.
United States Patent |
6,254,954 |
Bennett , et al. |
July 3, 2001 |
**Please see images for:
( Certificate of Correction ) ** |
Pressure-sensitive adhesive tape
Abstract
The invention relates to a pressure-sensitive adhesive tape with
improved room temperature handleability comprising an adhesive
layer with at least one exposed surface and optionally a backing,
wherein the pressure-sensitive adhesive layer comprises an
epoxy/polyester based pressure sensitive adhesive which is
crosslinkable upon exposure to actinic or e-beam irradiation and
optionally heat, and comprises (i) 30-80% by weight of a polyester
component comprising one or more amorphous polyesters compounds,
(ii) 20-70% by weight of an epoxy component comprising one or more
epoxy resins and/or monomers, (iii) 0-50% by weight of a
hydroxyl-functional component containing one or more
hydroxyl-containing compounds having a hydroxyl functionality of at
least 1, and (iv) an effective amount of a photoinitiator component
for crosslinking the pressure-sensitive adhesive, whereby the
weight percentages refer to the total mass of components (i)-(iv)
and add up to 100 wt. %, and which exhibits a holding power of at
least 5 min.
Inventors: |
Bennett; Greggory S. (Hudson,
WI), George; Clayton A. (Afton, MN), Hitschmann;
Guido (Neuss, DE), Lamon; Alain H. (Le Pecq,
FR) |
Assignee: |
3M Innovative Properties
Company (St. Paul, MN)
|
Family
ID: |
23449310 |
Appl.
No.: |
09/367,958 |
Filed: |
August 26, 1999 |
PCT
Filed: |
February 28, 1997 |
PCT No.: |
PCT/US97/03170 |
371
Date: |
August 26, 1999 |
102(e)
Date: |
August 26, 1999 |
PCT
Pub. No.: |
WO98/38262 |
PCT
Pub. Date: |
September 03, 1998 |
Current U.S.
Class: |
428/41.8;
156/275.7; 522/109; 522/170; 522/66; 522/31; 522/111; 428/355EP;
156/330; 428/345 |
Current CPC
Class: |
C09J
167/00 (20130101); C09J 7/38 (20180101); C09J
7/10 (20180101); C09J 167/00 (20130101); C08L
2666/22 (20130101); C09J 2463/00 (20130101); Y10T
428/1476 (20150115); Y10T 428/2809 (20150115); C09J
2467/00 (20130101); C08L 2666/22 (20130101); Y10T
428/287 (20150115); C08L 71/00 (20130101); C08L
63/00 (20130101) |
Current International
Class: |
C09J
7/02 (20060101); C09J 7/00 (20060101); C09J
167/00 (20060101); C08L 71/00 (20060101); C08L
63/00 (20060101); B32B 027/04 (); B32B 027/16 ();
B32B 027/38 () |
Field of
Search: |
;428/41.8,345,355EP,413,414 ;522/31,66,109,111,170 ;525/438
;156/272.3,275.7,330 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
0 109 851 B1 |
|
Sep 1993 |
|
EP |
|
0 620 259 A3 |
|
Oct 1994 |
|
EP |
|
0 620 259 A2 |
|
Oct 1994 |
|
EP |
|
9400679 |
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Dec 1995 |
|
NL |
|
WO 98/38262 |
|
Sep 1998 |
|
WO |
|
Primary Examiner: Ball; Michael W.
Assistant Examiner: Tolin; Michael A.
Attorney, Agent or Firm: Knecht, III; Harold C.
Claims
What is claimed is:
1. Pressure-sensitive adhesive tape with improved room temperature
handleability comprising at least one pressure-sensitive adhesive
layer with at least one exposed surface and optionally a backing,
wherein the pressure-sensitive adhesive layer comprises an
epoxy/polyester based pressure sensitive adhesive comprising
(i) 30-80% by weight of a polyester component comprising one or
more amorphous polyester compounds;
(ii) 20-70% by weight of an epoxy component comprising one or more
epoxy resins and/or monomers;
(iii) 0-5% by weight of a hydroxyl-functional component comprising
one or more hydroxyl-containing compounds having a hydroxyl
functionality of at least 1; and
(iv) an effective amount of a photoinitiator component for
crosslinking the pressure-sensitive adhesive;
wherein the weight percentages refer to the total mass of
components (i)-(iv) and add up to 100% by weight and the
pressure-sensitive adhesive exhibits a holding power of at least 5
minutes and is crosslinkable, upon exposure to actinic or electron
beam irradiation, and optionally heat.
2. Pressure-sensitive adhesive tape according to claim 1 wherein
the amorphous polyester compounds exhibit a glass transition
temperature of between -20 and 50.degree. C.
3. Pressure-sensitive adhesive tape according to claim 1 wherein
the ratio of the sum of the masses of compounds of components
(i)-(iii) which are liquid at room temperature with respect to the
total mass of components (i)-(iii) is not more than 0.6.
4. Pressure-sensitive adhesive tape according to claim 1 wherein
the ratio of the sum of the masses of components (ii) and (iii)
with respect to the total mass of components (i)-(iv) is between
0.2 and 0.7.
5. Pressure sensitive adhesive tape according to claim 1 which
exhibits a 90.degree. peel adhesion value at room temperature on
stainless 20 minutes after application of at least 4 N/0.5
inch.
6. Pressure-sensitive adhesive tape according to claim 1 comprising
a photoinitiator component consisting of one or more
photoinitiators for cationic crosslinking.
7. Pressure-sensitive adhesive tape according to claim 6 wherein
the photoinitiator component comprises one or more photoinitiators
selected from the group consisting of aromatic onium complex salts
and metallocene salts.
8. Pressure-sensitive adhesive tape according to claim 1 wherein
the hydroxyl-functional component comprises one or more compounds
selected from the group consisting of bisphenal-A extended polyols,
polyol adducts of glycol and propylene oxides, polycaprolactam
based polyols and polytetrahydrofuran based polyols.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive tape
with improved room temperature handleability comprising at least
one adhesive layer with at least one exposed surface and optionally
a backing, wherein the pressure-sensitive adhesive layer comprises
an epoxy/polyester based pressure-sensitive adhesive which is
crosslinkable upon exposure to actinic or e-beam irradiation. The
invention furthermore refers to a method of bonding a first
substrate to a second substrate by using such pressure-sensitive
adhesive tape and to the assembly prepared by such method.
2. Description of the Related Art
U.S. Pat. No. 4,920,182 describes UV-activatable curable
compositions comprising one or more epoxy resins having an average
of at least two 1,2-epoxy groups per molecule, one or more flexible
polyesters which are terminated by, on average, at least two
carboxyl groups, and a metallocene complex initiator. The
composition, which can be used for the production of surface
coatings on a variety of substrates or as an adhesive, can be cured
by the application of heat or with a combination of irradiation and
heat. The curing temperature is generally 40-200.degree. C.,
preferably 80-110.degree. C.
U.S. Pat. No. 4,256,828 describes photocopolymerizable compositions
which contain epoxides, organic material with hydroxyl
functionality such as hydroxyl-terminated polyesters, and a
photosensitive aromatic sulfonium or iodonium salt of a
halogen-containing complex ion. The compositions can be used in a
variety of applications, for example, as photocurable ink vehicles,
binders for abrasive particles, paints, adhesives, coatings for
lithographic and relief printing plates, protective coatings for
metals, wood, etc. The compositions are typically coated onto the
respective surface, and are photocurable at room temperature or
below.
The curable hot melt compositions of European Patent Publication
No. 0,620,259 comprise an epoxy component, a polyester component, a
photoinitiator and optionally a hydroxyl-containing material. The
hot melt compositions, which can be tacky or non-tacky, may be
applied to a variety of substrates by extruding, spraying, gravure
printing or coating (e.g. by using a coating die, a heated knife
blade coater, a roll coater or a reverse roll coater). The hot melt
composition may also be applied as an uncured, free-standing
adhesive film which, when used to bond a first substrate, may be
irradiated on one or both sides and then placed between two
substrates by the use of heat, pressure or both heat and pressure
to bond the film to the two substrates. Alternatively, it is
possible to laminate the hot melt adhesive film to a backing at
room temperature using a pressure of, for example, 10 psi as is
suggested in U.S. Pat. No. 5,436,063. This reference describes a
coated abrasive article comprising a backing, a first binder on the
backing, a plurality of abrasive particles in the first binder, and
a second binder over the first binder and the abrasive particles.
The first binder is a photocurable hot-melt adhesive as described
in European Patent Publication No. 0,620,259.
While the crosslinkable hot melt epoxy/polyester based adhesives
described above have broad utility, there are certain, specific
applications where improved mechanical integrity and/or cohesive
strength are desired or required. Therefore there is a need for a
crosslinkable epoxy/polyester based pressure-sensitive adhesive
materials available to the person skilled in the art to allow him
or her to select appropriate adhesive materials exhibiting
advantageous properties for a specific application and, in
particular, for the preparation of unsupported and supported
pressure-sensitive adhesive tapes with improved and/or convenient
handleability at room temperature or below. Other objects of the
present invention can be taken from the detailed specification
below.
BRIEF DESCRIPTION OF THE INVENTION
The present invention refers to a pressure-sensitive adhesive tape
with improved room temperature handleabilty comprising at least one
pressure-sensitive adhesive layer with at least one exposed surface
and optionally a backing, wherein the pressure-sensitive adhesive
layer comprises an epoxy/polyester based pressure sensitive
adhesive which is crosslinkable upon exposure to actinic or e-beam
irradiation and which comprises:
(i) 30-80% by weight of a polyester component comprising one or
more amorphous polyester compounds;
(ii) 20-70% by weight of an epoxy component comprising one or more
epoxy resins and/or monomers;
(iii) 0-50% by weight of a hydroxyl-functional component containing
one or more hydroxyl-containing compounds having a hydroxyl
functionality of at least 1; and
(iv) an effective amount of a photoinitiator component for
crosslinking the pressure-sensitive adhesive;
wherein the weight percentages refer to the total mass of
components (i)-(iv) and add up to 100% by weight, and further
wherein the pressure-sensitive adhesive which exhibits a holding
power of at least 5 minutes.
The present invention furthermore refers to a method of bonding a
first substrate to a second substrate with a pressure-sensitive
adhesive tape according to the invention having two exposed
adhesive surfaces. The method comprises the steps of applying the
first exposed surface of the pressure-sensitive adhesive to the
first substrate and attaching the second substrate to the second
exposed surface of the pressure-sensitive adhesive whereby the
pressure-sensitive adhesive layer according to the invention is
subjected to actinic or e-beam irradiation and, optionally, heat
prior to bonding them to the respective substrate within the
after-cure bonding time or after bonding them to the respective
substrates. The invention furthermore refers to assemblies which
are obtainable by such method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The term pressure-sensitive adhesive tape as referred to above and
below describes supported or unsupported, essentially
two-dimensional articles such as sheets, strips, ribbons or die-cut
parts (i.e., the extension of the articles in two directions
distinctly exceeds the extension in the third direction):
(i) which are tacky at room temperature and can be applied to a
wide variety of substrates by exerting, for example, finger
pressure, and
(ii) which can be conveniently handled at lower temperatures such
as room temperature without breaking, i.e., which exhibit a
sufficiently high internal strength and cohesivity and a certain
elasticity so that removable liners can easily be stripped off the
tape without damaging the tape, and the tape can at least be
slightly stretched and transferred to the substrate by hand.
Feature (i) requires an initial 90.degree. peel adhesion value on
stainless steel as measured 20 minutes after application onto the
substrate according to the test method specified below of at least
4N/inch or more.
Feature (ii) requires a holding power time as measured according to
the test method specified in the experimental part below, of at
least 5 minutes or more.
The epoxy/polyester based presssure-sensitive adhesive tapes
according to the present invention are crosslinkable and can be
converted to crosslinked pressure-sensitive adhesive tapes upon
exposure to actinic or e-beam irradiation and, optionally, heat.
The crosslinked pressure-sensitive adhesive may bond, for example,
2 substrates, and the resulting configuration is termed as an
assembly.
The term adhesive film as referred to above and below describes
two-dimensional articles which may be tacky or non-tacky at room
temperature and exhibit a debonding time of less than 5 min. and,
in particular, of not more than 3 minutes.
The pressure-sensitive adhesive tapes of the present invention
which may be supported or unsupported, exhibit at least one
pressure-sensitive adhesive layer comprising an epoxy/polyester
based pressure-sensitive adhesive.
It was found by the present inventors that for imparting improved
room temperature handleability to the pressure-sensitive adhesive
tapes it is essential that the polyester component (i) of the
pressure-sensitive adhesive comprises one or more amorphous
polyester compounds. Amorphous polyesters are differentiated from
crystalline polyesters in that they do not display a measurable
crystalline melting point when subjecting a sample of about 8 mg to
a DSC (differential scanning calorimetry) scan at a rate of
20.degree. C./min. from -60.degree. C. to 200.degree. C. The DSC
measurements are preferably performed by using commercially
available DSC equipment such as, for example, a DSC7 differential
scanning calorimeter from Perkin Elmer, Norwalk, Conn., U.S.A.
While not displaying a crystalline melting point when being subject
to the DSC scan described above, the amorphous polyester compounds
exhibit a glass transition temperature which preferably is between
-20.degree. C. and 50.degree. C. Especially preferred are amorphous
polyester compounds with a glass transition temperature of between
-15.degree. C. and 25.degree. C. and, most preferred, of between 0
and 25.degree. C.
Amorphous polyester compounds which can be used for the preparation
of the tapes according to the present invention include both
hydroxyl- and carboxyl-terminated materials. The softening point
preferably is between 50 and 150.degree. C., more preferably
between 70 and 140.degree. C., and most preferably between 60 and
110.degree. C. The molecular weight is preferably adjusted to give
a melt flow rate at 200.degree. C. of between 10 and 300 g/min and
more preferably between 20 and 250 g/min. The melt flow rate is
measured according to DIN ISO 1133 by placing approximately 10 g of
the respective amorphous polyester compound in a
temperature-conditioned metal cylinder. Via a cylindrical die, a
force of 21.6 N acts on the melted sample. The amount of sample
which flows through a standardized nozzle within a certain time is
weighed and is converted to a flow rate given in g/min. Preferred
amorphous compounds also have a number average equivalent weight of
about 7,500 to 200,000 and more preferably from about 10,000 to
about 50,000 as determined by GPC (gel permeation chromatography)
in THF (tetrahydrofuran) calibrated with polystyrene standards.
Polyester compounds which are useful for the preparation of the
tapes according to the present invention can be obtained, for
example, as the reaction product of dicarboxylic acids (or their
diester equivalents) and diols. Examples of aliphatic dicarboxylic
acids are saturated aliphatic dicarboxylic acids, such as oxalic
acid, malonic acid, succinic acid, .alpha.-methylsuccinic acid,
glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic
acid or dimerized linoleic acid; or unsaturated aliphatic
polycarboxylic acids, such as maleic acid, fimaric acid, mesaconic
acid, citraconic acid, glutaconic acid or itaconic acid, and also
possible anhydrides of these acids. Examples of cycloaliphatic
dicarboxylic acids are hexahydrophthalic, hexahydroisophthalic or
hexahydroterephthalic acid, tetrahydrophthalic,
tetrahydroisophthalic of tetrahydroterephthalic acid or
4-methyltetrahydrophthalic acid, 4-methylhexahydrophthalic acid or
endomethylenetetrahydrophthalic acid. Examples of aromatic
dicarboxylic acids are phthalic, isophthalic and terephthalic acid.
Examples of polyfunctional carboxylic acids are aromatic
tricarboxylic or tetracarboxylic acids, such as trimellitic acid,
trimesic acid, pyromellitic acid or benzophenonetetracarboxylic
acid; or trimerized fatty acids or mixtures of dimerized and
trimerized fatty acids, such as are available commercially, for
example, under the trade name Pripol.RTM.. Blends of any of the
foregoing diacids or polyacids may also be used.
Examples of suitable aliphatic diols are
.alpha.,.omega.-alkylenediols, such as ethylene glycol,
propane-1,2-diol, propane-1,3-diol, butane-1,4-diol,
pentane-1,5-diol, neopentyl glycol, hexane-1,6-diol,
octane-1,8-diol, decane-1,10-diol or dodecane-1,12-diol. Examples
of suitable cycloaliphatic diols are 1,3-dihydroxycyclohexane,
1,4-dihydroxycyclohexane, 1,4-cyclohexanedimethanol,
bis-4-(hydroxycyclohexyl)-methane or
2,2-bis-(4-hydroxycyclohexyl)-propane. Examples of suitable
polyfunctional alcohols are 1,1,1-trimethylolethane,
1,1,1-trimethylolpropane, glycerol or pentaerythritol. Long chain
diols including poly (oxyalkylene) glycols in which the alkylene
group preferably contains from 2 to 9 carbon atoms (more preferably
from 2 to 4 carbon atoms) may also be used. Blends of any of the
foregoing diols or polyols may also be used.
The examples of di- or polycarboxylic acids, esters or anhydrides,
and di- or polyhydroxylic compounds are merely to illustrate the
invention without limiting it.
Reacting, for example, the dicarboxylic acids (or their diester
equivalents) and the diols enumerated above may result in amorphous
and/or semicrystalline polyesters. Amorphous polyester compounds
can be easily identified by subjecting them to a DSC scan as was
described above. Amorphous rather than crystalline polyester
compounds can be obtained, for example, by reacting adducts with a
high degree of stereo-irregularity which cannot effectively pack
into crystalline structures and impart a high degree of entropy to
the resulting polymer. Details on the preparation of amorphous
polymers can be found, for example, in Encyclopedia of Polymer
Science and Engineering, New York 1988, vol. 12, pp. 1-312 and the
references cited therein, and in the Polymeric Materials
Encyclopedia, Boca Raton 1996, vol. 8, pp. 5887-5909 and the
references cited therein.
Amorphous polyester compounds are also commercially available, for
example, from Huls AG, Marl, Germany, as Dynapol S 1606, S 1611, S
1426, S 1427, S 1313, S 1421, and S 1420 with Dynapol S 1313, S
1421 and S 1420 being preferred.
The polyester component (i) of the pressure-sensitive adhesive of
the present invention can also comprise a small amount of
crystalline polyester compounds.
The pressure-sensitive adhesive used for the preparation of the
pressure-sensitive adhesive tapes according to the invention
further comprises an epoxy component (ii) containing one or more
organic compounds having an oxirane ring polymerizable by ring
opening. Such compounds, broadly called epoxides, include monomeric
epoxy compounds and epoxides of the polymeric type and can be
aliphatic, cycloaliphatic, aromatic or heterocyclic. Monomeric and
oligomeric epoxy compounds preferably have at least two and more,
preferably two to four, polymerizable epoxy groups per molecule. In
polymeric type epoxides or epoxy resins, there may be many pendent
epoxy groups (e.g., a glycidyl methacrylate polymer could have
several thousand pendent epoxy groups per average molecular
weight). Oligomeric epoxides and, in particular, polymeric epoxy
resins are preferred.
The molecular weight of the epoxy-containing materials (ii) may
vary from low molecular weight monomeric or oligomeric materials
with a molecular weight, e.g., from about 100 to polymeric resins
with a molecular weight of about 50,000 or more and may vary
greatly in the nature of their backbone and substituent groups. For
example, the backbone may be of any type, and substituent groups
thereon can be any group not having a nucleophilic group or
electrophilic group (such as an active hydrogen atom) which is
reactive with an oxirane ring or which substantially inhibits
cationic polymerization. Illustrative of permissible substituent
groups are halogens, ester groups, ethers, sulfonate groups,
siloxane groups, nitro groups, amide groups, nitrile groups,
phosphate groups, etc. Mixtures of various epoxy-containing
compounds can also be used in the epoxy part (ii) of the precursor
of this invention. The epoxy component (ii) preferably comprises a
mixture of two or more epoxy resins in order to modify and adapt
the mechanical properties of the cured adhesive with respect to
specific requirements.
The term "epoxy resin" is used herein to mean any of dimeric,
oligomeric or polymeric epoxy materials containing a plurality,
i.e. at least 2, of epoxy functional groups. Types of epoxy resins
that can be used include, for example, the reaction product of
bisphenol A and epichlorohydrin, the reaction product of phenol and
formaldehyde (novolac resin) and epichlorohydrin, peracid epoxies,
glycidyl esters, the reaction product of epichlorohydrin and
p-amino phenol, the reaction product of epichlorohydrin and glyoxal
tetraphenol and the like.
Suitable commercially available diglycidic ethers of bisphenol-A
are Ciba Geigy Araldite.TM. 6010, Dow Chemical DER.TM. 331, and
Shell Chemical Epon.TM. 825, 828, 826, 830, 834, 836, 1001, 1004,
1007, etc. A polyepoxidized phenol formaldehyde novolac prepolymer
is available from Dow Chemical as DEN.TM. 431 and 438 and from Ciba
Geigy as CY-281.TM., and a polyepoxidized cresol formaldehyde
novolac prepolymer is available from Ciba Geigy as ECN.TM. 1285,
1280 and 1299. A polyglycidyl ether of polyhydric alcohol is
available from Ciba Geigy, based on butane-1,4-diol, as
Araldite.TM. RD-2; and from Shell Chemical Corporation based on
glycerine, as Epon.TM. 812. Suitable commercially available
flexible epoxy resins include polyglycol diepoxies, DER.TM. 732 and
736, from Dow Chemical Company, diglycidyl ester of linoleic dimer
acid, Epon.TM. 871 and 872 from Shell Chemical Company, diglycidyl
ester of a bisphenol in which the aromatic rings are linked by a
long aliphatic chain, Lekutherm.TM. X-80, from Mobay Chemical
Company, epoxidized synthetic rubber materials which are available
from Shell Chemical Corporation and epoxidized natural rubber
materials such as ENR-10, ENR-25 and ENR-50 which are available
from the Rubber Research Institute of Malaysia. The ENR materials
are described in Encyclopedia of Polymer Science and Engineering,
New York 1988, vol. 14, p. 769.
High functional epoxy resins (i.e. functionality greater than 2)
which can be used include, for example, a solid epoxy novolac
resin, DEN.TM. 485 from Dow Chemical Company, a tetrafunctional
solid epoxy resin, Epon.TM. 1031 from Shell Chemical Company, and
N,N,N',N'-tetraglycidyl-4,4'-methylenebisbenzenamine, Araldite.TM.
720 from Ciba Corporation. Difunctional epoxy resins which can be
used include, for example, a solid resin,
N,N,N',N',-tetraglycidyl-a,A'-bis(4-aminophenyl)-p-diisopropylbenzene,
HPT.TM. 1071 from Shell Company, solid diglycidyl ether of
bisphenol-9fluorene, HPT.TM. 1079 from Shell Chemical Company, and
triglycidylether of paraaminophenol, Araldite.TM. 0500/0510 from
Ciba-Geigy Corporation.
Useful cycloaliphatic epoxy resins include, for example,
vinylcyclohexane dioxide which is commercially available as
ERL-4206 from Union Carbide Corp.,
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate
commercially available as ERL-4221 from Union Carbide Corp.,
3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclo hexane
carboxylate commercially available as ERL-4201 from Union Carbide
Corp., bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate commercially
available as ERL-4289 from Union Carbide Corp. or
bis(2,3-epoxycyclopentyl)ether commercially available as ERL-0400
from Union Carbide Corp.
The pressure-sensitive adhesive used for the preparation of the
pressure-sensitive adhesive tapes according to the present
invention furthermore comprises as component (iv) a photoinitiator
component comprising an effective amount of one or more
photoinitiator compounds. The photopolymerization may be performed
at room temperature or below but may also be performed at higher
temperatures which preferably are lower than the melting
temperature of the pressure-sensitive adhesive tape, in order to
accelerate the crosslinking reaction.
The photopolymerization is preferably performed as cationic
polymerization, and the photoinitiators are preferably selected
from a group consisting of metallocene salts and aromatic onium
salts. Suitable salts of organometallic complex cations (or
metallocene salts) include but are not limited to, those salts
having the following formula (I)
wherein
M.sup.p represents a metal ion selected from the group consisting
of Cr, Mo, W, Mn Re, Fe. and Co with p denoting the charge of the
metal ion;
L.sup.1 represents 1 or 2 ligands contributing pi-electrons that
can be the same or different ligand selected from the group of:
substituted and unsubstituted .eta..sup.3 -allyl, .eta..sup.5
-cyclopentadienyl, and .eta..sup.7 -cycloheptatrienyl, and
.eta..sup.6 -aromatic compounds selected from .eta..sup.6 -benzene
and substituted .eta..sup.6 -benzene compounds and compounds having
2 to 4 fused rings, each capable of contributing 3 to 8
pi-electrons to the valence shell of M.sup.p ;
L.sup.2 represents none, or 1 to 3 ligands contributing an even
number of sigma-electrons that can be the same or different ligand
selected from the group of: carbon monoxide, nitrosonium, triphenyl
phosphine, triphenyl stibine and derivatives of phosphorus, arsenic
and antimony, with the proviso that the total electronic charge
contributed to
M.sup.p results in a net residual positive charge of q to the
complex;
q is an integer having a value of 1 or 2, the residual charge of
the complex cation;
Y is halogen-containing complex anion selected from BF.sub.4.sup.-,
AsF.sub.6.sup.-, PF.sub.6.sup.-, SbF.sub.5 OH.sup.-,
SbF.sub.6.sup.-, and CF.sub.3 SO.sub.3.sup.- ; and
n is an integer having a value of 1 and 2, the number of complex
anions required to neutralize the charge q on the complex
cation.
Preferred examples of suitable salts of organometallic complex
which are cations useful in the pressure-sensitive adhesive tape of
the invention include the following:
(.eta..sup.6 -benzene)(.eta..sup.5 -cyclopentadienyl)iron(+)
hexafluoroantimonate
(.eta..sup.6 -toluene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroarsenate
(.THETA..sup.6 -cumene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexaflurorphosphate
(.eta..sup.6 -p-xylene)(.eta..sup.5 -cyclopentadienyl)iron (1+)
hexafluoroantinomate
(.eta..sup.6 -xylenes)(mixed isomers)(.eta..sup.5
-cyclopentadienyl)iron (1+) hexafluorophosphate
(.eta..sup.6 -o-xylene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
triflate
(.eta..sup.6 -m-xylene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
tetrafluoroborate
(.eta..sup.6 -mesitylene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -hexamethylbenzene)(.eta..sup.5
-cyclopentadienyl-)iron(1-) pentafluorohydroxyantimonate
(.eta..sup.6 -naphthalene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
tetrafluoroborate
(.eta..sup.6 -pyrene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
triflate
(.eta..sup.6 -toluene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -cumene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -p-xylene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -m-xylene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -hexamethylbenzene)(.eta..sup.5
-cyclopentadienyl-)iron(1+) hexafluoroantimonate
(.eta..sup.6 -naphthalene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -pyrene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -chrysene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -perylene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
(.eta..sup.6 -chrysene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
pentafluorohydroxyantimonate
(.eta..sup.6 -acetophenone)(.eta..sup.5
-methylcyclopentadienyl-)iron(1+) hexafluoroantimonate
(.eta..sup.6 -fluorene)(.eta..sup.5 -cyclopentadienyl)iron(1+)
hexafluoroantimonate
Metallocene salts of formula I and their preparation are described,
for example, in U.S. Pat. No. 5,089,536, U.S. Pat. No. 5,059,701
and European Patent Publication No. 0,109,851. The metallocene
salts may be used in conjunction with a reaction accelerator such
as an oxalate ester of a tertiary alcohol.
Also preferred are aromatic onium salts which are disclosed, for
example in U.S. Pat. Nos. 4,069,054, 4,231,951 and 4,250,203. Such
salts can be described by the formula:
wherein
A is an organic cation selected from those described in U.S. Pat.
Nos. 3,708,296, 3,729,313, 3,741,769, 3,794,576, 3,808,006,
4,026,705, 4,058,401, 4,069,055, 4,101,513, 4,216,288, 4,394,403,
and 4,623,676, all incorporated herein by reference, and
X is an anion where X is defined as Y in formula (I) above.
A is preferably selected from diazonium, iodonium, and sulfonium
cations and more preferably from diphenyliodonium,
triphenylsulfonium and phenylthiophenyl diphenylsulfonium. X
preferably is selected from the group of anions consisting of
CF.sub.3 SO.sub.3.sup.-, BF.sub.4.sup.-, PF.sub.6.sup.-,
SbF.sub.6.sup.-, SbF.sub.6 OH.sup.-, AsF.sub.6.sup.-, and
SbCl.sub.6.sup.-.
Aromatic iodonium salts and aromatic sulfonium salts are preferred.
Especially preferred aromatic iodonium and aromatic sulfonium salts
are described in European Patent Publication No. 0,620,259, p. 5,
In. 17 to p. 6, In. 29.
Useful commercially available cationic photoinitiators include UVOX
UVI-6974, an aromatic sulfonium complex salt (Union Carbide Corp.),
and IRGACURE 261, a metallocene complex salt (Ciba-Geigy).
The pressure-sensitive adhesives which are useful for the
preparation of pressure-sensitive adhesive tapes according to the
invention optionally comprise a hydroxyl-functional component (iii)
containing one or more hydroxyl-containing compounds having a
hydroxyl functionality of at least 1, and more preferably of at
least 2. The hydroxyl-containing compounds should be substantially
free of other "active hydrogen" containing groups such as amino and
mercapto moieties. The hydroxyl-containing compounds should also be
substantially free of groups which may be thermally and/or
photolytically unstable so that the compounds will not decompose or
liberate volatile components when exposed to e-beam or actinic
radiation and, optionally, to heat during curing. Preferably the
compounds contain two or more primary or secondary aliphatic
hydroxyl groups (i.e., the hydroxyl group is bonded directly to a
non-aromatic carbon atom). The hydroxyl group may be terminally
situated, or may be pendent from a polymer or copolymer. The number
average equivalent weight of the hydroxyl-containing material is
preferably about 31 to 2500, more preferably about 80 to 1000, and
most preferably about 80 to 350.
The hydroxyl number which can be described by the equation:
##EQU1##
wherein
OH=hydroxyl number of the hydroxyl functional compound;
f=functionality, that is, average of hydroxyl groups per molecule
of hydroxyl functional compound; and
m.w.=molecular weight of the hydroxyl functional compound (number
average).
Illustrative examples of hydroxyl-containing materials include both
monomeric and polymeric compounds. Monomeric hydroxyl-functional
compounds comprise, for example, such as ethylene glycol, propylene
glycol, 1,3-dihydroxypropane, 1,3-dihydroxybutane,
1,4-dihydroxybutane, 1,4-, 1,5-, and 1,6-dihydroxyhexane, 1,2-,
1,3-, 1,4-, 1,6-, and 1,8-dihydroxyoctane, 1,10-dihydroxyhexane,
1,1,1-trimethylolethane, 1,1,1 -trimethylolpropane,
pentaerythritol, polycaprolactone, xylitol, arabitol, sorbitol or
mannitol. Suitable examples of polymeric hydroxyl-functional
compounds comprise, for example, polyoxyalkylene polyols (e.g.,
polyoxyethylene and polyoxypropylene glycols and triols of
equivalent weight of 31 to 2500 for the diols or 80 to 350 for
triols), polytetramethylene oxide glycols of varying molecular
weight, hydroxyl-terminated polyesters, and hydroxyl-terminated
polyacetones.
Useful commercially available hydroxyl-containing materials include
the POLYMEG series (available from QO Chemicals, Inc.) of
polytetramethylene oxide glycols such as POLYMEG 650, 1000 and
2000; the TERATHANE series (from E.I. duPont de Nemours and
Company) of polytetramethylene oxide glycols such as TERATHANE 650,
1000 and 2000; POLYTHF, a polytetramethylene oxide glycol from BASF
Corp.; the BUTVAR series (available from Monsanto Chemical Company)
of polyvinylacetal resins such as BUTVAR B-72A, B-73, B-76, B-90
and B-98; the TONE series (available from Union Carbide) of
polycaprolactone polyols such as TONE 0200, 0210, 0230, 0240, and
0260; the DESMOPHEN series (available from Miles Inc.) of saturated
polyester polyols such as DESMOPHEN 2000, 2500, 2501, 2001KS, 2502,
2505, 1700, 1800, and 2504; the RUCOFLEX series (available from
Ruco Corp.) of saturated polyester polyols such as S-107, S-109,
S-011 and S-1014; VORANOL 234-630 (a trimethylol propane) from Dow
Chemical Company; VORANOL 230-238 (a glycerol polypropylene oxide
adduct) from Dow Chemical Company; the SYNFAC series (from Milliken
Chemical) of polyoxyalkylated bisphenol A's such as SYNFAC 8009,
773240, 8024, 8027, 8026, and 8031; the ARCOL series (from Arco
Chemical Co.) of polyoxypropylene polyols such as ARCOL 425, 1025,
2025, 42, 112, 168, and 240; and the SIMULSOL series from Seppic,
Paris, France) of bisphenol-A extended polyols such as SIMULSOL
PHE, BPIE, BPJE, BPLE, BPNE, BPRE, BPHP, BPIP, BPRP and BPUP.
The amount of the polyester component (i) with respect to the total
mass of components (i)-(iv) is between 30 wt. %-80 wt. % and
preferably between 35 wt. % and 55 wt. %. The polyester component
comprises one or more polyester compounds and, in particular, from
1-4 polyester compounds at least one of them being an amorphous
polyester compound. Polyester components which only comprise
amorphous polyester compounds are preferred.
The amount of the epoxy component (ii) with respect to the total
mass of components (i)-(iv) is between 20 wt. % to 70 wt. %. The
epoxy component comprises at least one epoxy resin or epoxy
monomer, preferably from 1-4 and more preferably from 1-3 epoxy
resins and/or monomers. The epoxy compounds can be liquid or solid
at room temperature under normal conditions. It was found that the
softness of the pressure-sensitive adhesive at room temperature can
be varied by varying the glass transition temperature of the
polyester component (i) and the ratio of liquid and solid epoxy
compounds. In case the polyester component comprises more than one
polyester compound the glass transition temperature T.sub.g can be
well estimated using the Fox equation ##EQU2##
wherein T.sub.g,n is the glass transition temperature and X.sub.n
is the mole fraction, respectively, of the n-th polyester compound.
A full description of T.sub.g calculations based on the Fox
equation can be found in Makromolekuele, 5th Ed. by Hans-Georg
Elias (Huethig & Wepf, 1990), p. 856.
In case the glass transition temperature of the polyester component
(i) is less than 0.degree. C., the ratio m.sub.L /m.sub.S of the
sum of the masses of liquid epoxy compounds and liquid
hydroxyl-functional compounds over the sum of the masses of solid
epoxy compounds and solid hydroxyl-functional compounds preferably
is not more than 1.2 and especially preferably lower than 0.50. In
case the glass transition temperature of the polyester component is
above 0.degree. C., and, in particular, above 10.degree. C., the
ratio of the masses of liquid epoxy compounds and liquid
hydroxyl-functional compounds over the masses of solid epoxy
compounds and solid hydroxyl-functional compounds preferably is
greater than 0.5, more preferably greater than 1 and most
preferably greater than 2.
It was also found that the 90.degree. peel adhesion of the
pressure-sensitive adhesive on stainless steel can be modified and
adapted to specific needs by varying the ratio m.sub.L /m.sub.S for
a given T.sub.g of the polyester component. The initial peel
adhesion on stainless steel as measured 20 minutes after
application of the pressure-sensitive adhesive tape can usually be
increased in case the glass transition temperature of the polyester
component is less than 0.degree. C. by decreasing the above ratio
m.sub.L /m.sub.S as long as phase separation of the
pressure-sensitive adhesive is avoided. In case the glass
transition temperature of the polyester component is above
0.degree. C., the initial peel adhesion can also generally be
increased by decreasing the above ratio m.sub.L /m.sub.S as long as
m.sub.L /m.sub.S >1 whereas when decreasing the ratio m.sub.L
/m.sub.S in the area m.sub.L /m.sub.S.ltoreq.1, an increase in peel
adhesion is usually observed.
The amount of the optional hydroxyl-functional component (iii) with
respect to the total mass of components (i)-(iv) is between 0-50
wt. % and preferably between 5-35 wt. %.
The hydroxyl-functional component if present, preferably comprises
from 1-3 and more preferably 1 or 2 compounds. The
hydroxyl-functional compounds can be solid or liquid at room
temperature under normal conditions but they are preferably liquid.
The amount of the hydroxyl-functional component is preferably
chosen so that the combined mass of the epoxy component (ii) and
the hydroxyl-functional component (iii) with respect to the total
mass of components (i)-(v) is ##EQU3##
wherein m.sub.n is the mass of the n-th compound and n is i, ii,
iii and iv. This ratio more preferably is between 0.3 and 0.55.
It was also found that the ratio m.sub.(ii)+(iii) /m.sub.(i) of the
sum of the masses of liquid and solid epoxy compounds and liquid
and solid hydroxyl functional compounds over the mass of the
polyester compounds preferably is less than 1.7, more preferably
less than than 1.6 and, in particular, less than 1.55. If the above
ratio is more than 1.75 and, in particular, at least 1.8 the
elasticity of the crosslinkable pressure-sensitive adhesive tape is
insufficient and the holding power tends to be less than 5
minutes.
The glass transition temperature of the pressure-sensitive adhesive
as measured by the peak in the 1 Hz tan delta curve when cooling
the sample from a temperature about 50.degree. C. above its T.sub.g
to a temperature about 50.degree. C. below its T.sub.g at a rate of
2.degree. C./min using a Rheometrics RDA 11 in the parallel plate
shear strain mode, is preferably between -15.degree. C. and
30.degree. C., more preferably between 0.degree. C. and 25.degree.
C.
The T.sub.g of the pressure-sensitive adhesive can be modified by
controlling T.sub.g of the polyester compound(s) and/or the above
ratio m.sub.L /m.sub.S. Increasing the amount of polyester
compound(s) with a lower value of T.sub.g tends to decrease the
T.sub.g value of the pressure-sensitive adhesive. Increasing the
ratio m.sub.L /m.sub.S results in lowering the T.sub.g of the
pressure-sensitive adhesive while decreasing the ratio m.sub.L
/m.sub.S tends to raise T.sub.g of the pressure-sensitive
adhesive.
It is preferred that the pressure-sensitive adhesive does not
exhibit macroscopic phase separation. By macroscopic phase
separation it is meant that components of the pressure-sensitive
adhesive tape migrate to the release liner protecting the exposed
adhesive surfaces, and result in an easily visible haze on the
release liner after it is removed from the pressure-sensitive
adhesive tape.
The amount of the photoinitiator component (iv) with respect to the
total mass of components (i)-(iv) is preferably between 0.01-5% by
weight and more preferably between 0.1-2% by weight. The
photoinitiator component preferably comprises 1-3 and, more
preferably, 1 photoinitiator compound.
The mass percentages given for components (i)-(iv) of the
pressure-sensitive adhesive add up to give 100 wt. %.
The pressure-sensitive adhesive may additionally comprise various
fillers, adjuvants, additives and the like such as silica, glass,
clay, talc, pigments, colorants, glass beads or bubbles, glass or
ceramic fibers, antioxidants, flame retardants and the like so as
to reduce the weight or cost of the composition, adjust viscosity,
and provide additional reinforcement. Fillers and the like which
are capable of absorbing the radiation used during the curing
process should be used in an amount that does not adversely affect
the curing process. The amount of such additives may be between
0-50 wt. % and more preferably 0-15 wt. % with respect to the total
mass of components (i)-(iv).
The pressure-sensitive adhesive useful for the preparation of the
pressure-sensitive adhesive tapes of the present invention exhibits
a holding power value as measured according to the modified version
of PSTC-14 described in the test section below, of at least 5 min.,
preferably of at least 10 min. and more preferably of at least 20
min. which allows for the preparation of pressure-sensitive
adhesive tapes with improved room temperature handling properties.
Unsupported pressure-sensitive adhesive tapes of the present
invention with a thickness of, for example, 200 .mu.m exhibit a
certain elasticity and an elongation at break of typically 200% or
more.
The pressure-sensitive adhesive used for the preparation of the
pressure-sensitive adhesive tapes of the present invention exhibits
a 90.degree. peel adhesion at room temperature on stainless steel
20 minutes after application of at least 2N/0.5 inch, preferably at
least 4 N/0.5 inch, more preferably of at least 6 N/0.5 inch and
especially preferably of at least 7.5 N/0.5 inch. The peel adhesion
can be modified and optimized with respect to a specific
application by varying
the glass transition temperature of the amorphous polyester
component (i),
the ratio of liquid epoxy/solid epoxy compounds,
the amount of the optional hydroxyl functional component (iii),
and/or
the ratio of liquid/solid hydroxyl functional compounds
the molecular weight of the components
as was discussed above without adversely affecting the required
mechanical integrity and room temperature handleability of the
pressure-sensitive adhesive tape.
The pressure-sensitive adhesive tapes according to the present
invention can be unsupported or supported.
Unsupported pressure-sensitive adhesive tapes comprising no backing
(also termed as transfer tapes) can be obtained, for example, by
mixing components (i)-(iii) and, if present, additional fillers,
adjuvants or other additives in a suitable glass vessel at elevated
temperatures sufficient to liquify the mixture. The mixture is then
homogenized with a stirrer and the photoinitiator component (iv) is
added. The resulting mixture is then coated with the desired
thickness onto a first release liner such as a siliconized
polyester film, and a second release liner is subsequently
laminated onto the exposed surface of the unsupported
pressure-sensitive adhesive tape. Adding the photoinitiator
component (iv) shortly before coating avoids or minimizes
degradation of the photoinitiator compounds and/or premature
cationic polymerization. The method of preparation of unsupported
pressure-sensitive adhesive tapes outlined above illustrates the
invention only without limiting it. Other methods can be used such
as, for example, extruding the unsupported adhesive tape onto a
backing which may be, for example, a release liner.
Supported pressure-sensitive adhesive tapes comprise at least one
backing. Depending on the respective application, the backing may
be selected from a group of materials comprising polymeric films of
various stiffness such as, for example, polyolefins, polyesters,
polycarbonates or polymethacrylates, papers, non-wovens, one part
mechanical fasteners (which are described, for example, in U.S.
Pat. No. 5,077,870) or metals. The thickness of the backing
typically varies between 25 .mu.m and 3,000 .mu.m, preferably
between 25 and 1,000 .mu.m. The backing material should be selected
such that the layers of the adhesive bond very strongly to it. Such
a choice can be made easily and does not require any inventive
input from the expert. If desired, the backing may be treated with
chemical primers or may be corona treated.
The pressure-sensitive adhesive can be applied to the backing by
coating the molten mixture comprising components (i)-(iv) and, if
present, additional fillers, adjuvants or other additives.
Because of its advantageous cohesive strength and holding power
values, the pressure-sensitive adhesive used in the present
invention allows for preparing unsupported pressure-sensitive
adhesive tapes. The unsupported pressure-sensitive adhesive tapes
can be used, for example, for assembling two substrates. The
adhesive tape can be cut or die-cut to the desired geometrical
shape and applied to the first substrate at room temperature using
fingertip pressure or a suitable pressure-transferring device.
The curing reaction can be initiated, for example, by exposing the
pressure-sensitive adhesive tape to actinic radiation (i.e.,
radiation having a spectrum in the UV or VIS spectral regions which
at least partly overlaps the absorbence spectrum of the
photoinitiator compounds) or electron beam radiation. Preferably,
the energy is actinic radiation having a wavelength in the
ultraviolet or visible spectral regions. Suitable sources of
actinic radiation include mercury, xenon, carbon arc, tungsten
filament lamps, sunlight, etc. Ultraviolet radiation, especially
from a medium pressure mercury arc lamp, is especially preferred.
Preferred radiation sources have an essential part of their
spectral output in the wavelength range from 200-600 nm, more
preferably from 250-450 nm and most preferably from 300-450 nm.
Exposure times may be from less than about 1 second to 10 minutes
or more (to provide a total energy exposure of typically between 25
and 2,000 mJ/cm.sup.2 of UV-A energy measured by an appropriate
photo detection device such as those obtained from EIT (Sterling,
Va.) and calibrated according to N.I.S.T. (National Institute of
Standards and Technology) standards depending on both the amount
and the type of reactants involved, the energy source, the distance
from the energy source, the thickness of the adhesive tape and the
desired after-cure handling time.
The pressure-sensitive adhesive tapes may also be cured by exposure
to electron beam (e-beam) radiation. The dosage necessary is
generally from less than 1 megarad to 100 megarads or more. The
rate of curing tends to increase with increasing amounts of
initiator at a given energy exposure. The rate of curing also
increases with increased energy intensity.
Subsequent to the initiation of the cationic curing reaction the
second substrate is adhered to the pressure-sensitive adhesive
tapes using pressure within the after-cure handling time. The
after-cure handling time gives the time during which the respective
substrate can be reliably adhered to the curing pressure-sensitive
adhesive surface of the adhesive tape. With increasing crosslink
density of the pressure-sensitive adhesive the wet-out properties
of the adhesive tape with respect to the surface decrease and the
desired mechanical properties of the assembly such as high values
of overlap shear strength and/or impact strength may not be
obtained any longer. The after-cure handling time depends on the
properties of the pressure-sensitive adhesive used, the dose and
geometry of irradiation, the thickness of the pressure-sensitive
adhesive tape, the substrates and the desired properties of the
assembly. The after-cure handling time may vary from one second up
to 2 hours and is preferably between 2 and 15 minutes and more
preferably between 2 and 5 minutes.
The unsupported pressure-sensitive adhesive tape may also be
subjected to actinic and/or e-beam radiation prior to assembling it
to the substrates thus initiating the cationic curing reaction
prior to assembling. The actinic and/or e-beam radiation may be
applied to one or both sides of the pressure-sensitive adhesive
tape. Activating both sides of the pressure-sensitive adhesive tape
results in more homogeneously cured pressure-sensitive adhesive
tapes and is preferred. In case at least one of the substrates is
transparent, for example, to UV radiation, curing can be initiated
also after adhering the substrates to the pressure-sensitive
adhesive tape by shining the UV light through the UV transparent
substrate. If UV exposure is to only one side of the tape, it is
preferred that the UV source has a substantial UV emission between
300 and 400 nm to best ensure uniform curing.
The pressure-sensitive adhesive tape according to the invention can
be used for bonding a wide variety of substrates which may be
selected from a group of materials consisting of glass, plastics,
metals, ceramics and materials derived therefrom such as, for
example, ceramic coated glass. Depending on the substrates chosen
the mechanical properties of the cured assembly can sometimes be
improved by heating one or both of the substrates and/or the
pressure-sensitive adhesive tape after it has been applied to the
substrate or substrates, respectively. The temperatures applied are
preferably between 40 and 140.degree. C., and more preferably
between 80 to 120.degree. C. Although the present inventors do not
wish to be bound by such theory it is speculated that due to the
elevated temperature the wetting-out properties of the
pressure-sensitive adhesive tape at the interface substrate
surface/adhesive tape surface are improved which results in an
increased adhesion between substrate and tape. The heat applied to
the tape or the substrate preferably is kept low enough so as to
facilitate surface wet-out while avoiding that the entire
pressure-sensitive adhesive tape melts and becomes liquid. Heat
applied to the pressure-sensitive adhesive tape after it has been
activated, increases the rate of the epoxy curing reaction.
The heat treatment may be applied to one of both, respectively,
substrate/tape interfaces and it is also possible to keep the
assembly at an elevated temperature during the curing reaction in
order to decrease the curing time.
The assemblies according to the present invention are characterized
by advantageous mechanical properties and, in particular, by high
values of overlap shear strength and/or impact resistance as
measured according to the test methods specified below. Assemblies
of the present invention exhibiting an overlap shear strength of at
least 4 MPa, more preferably of at least 6 MPa and, in particular,
of at least 8 MPa are preferred. The impact resistance is
preferably at least 3 kJ/m.sup.2 and more preferably at least 6
kJ/m.sup.2 and most preferably at least 9 kJ/m.sup.2.
The pressure-sensitive adhesive tapes of the present invention are
useful for various applications such as, for example, bonding
applications in the automotive, construction or electronic
industries.
In a specific application an unsupported pressure-sensitive
adhesive tape of the present invention is used to adhere an
attachment means to a windscreen which allows for easy adjusting of
the windscreen when assembling it to the car body. The attachment
means may comprise, for example, a stud, clip, strip or another
fastener which is securely fastened or adhered to the windscreen by
using an unsupported or supported pressure-sensitive adhesive tape
of the present invention. The other end of the attachment means is
placed into predetermined points of the car body. In a specific
embodiment, the other end of the attachment means may pass through
a hole in the car body where it is mechanically fastened, for
example, by applying a nut to the attachment means or it may be
held in place by gravity and friction. Specific geometries of the
attachment means can be taken, for example, from U.S. Pat. No.
5,475,956. The attachment means may comprise various materials such
as, for example, metals such as brass, bronze, aluminum or steel,
and plastics such as PMMA (polymethylmethacrylate), polystyrene,
polyamide, polycarbonate, polyester or other rigid and moderately
polar plastics. In a particularly preferred embodiment, the
attachment means is an injection molded pin having a base member
approximately 2-3 cm in diameter, and a cylindrically shaped
positioning member essentially 2-3 cm long and 0.5-1 cm in
diameter, which is perpendicular to the base. The pin is preferably
made from PMMA or polyamide. A UV-crosslinkable pressure-sensitive
adhesive tape which preferably is unsupported, is unwound from a
roll, preferably in form of die-cuts, and subjected to UV
radiation. The first release liner is removed, and the activated
pressure-sensitive adhesive tape is attached to the rear surface of
the pin. After removal of the second release liner the pin is
attached to a predetermined position on the windscreen, preferably
to an area with a ceramic coating which has been pre-heated, for
example, with IR-heaters, to a surface temperature of at least
60.degree. C. and preferably at least 100.degree. C. It was found
that when subjecting the attachment means with the cured
pressure-sensitive adhesive after the windscreen had been assembled
to the car body, to a qualitative impact test (hitting with a
hammer onto the windscreen), this resulted in breaking of the
windscreen rather than any failure of the bond between windscreen
and pin.
The pressure-sensitive adhesive tape may also be used for adhering
oven brackets, for structural members or architectural
configurations or for bonding integrated circuit chips in
electronic industry.
The invention is further illustrated by the following, non-limiting
examples. First, however, certain procedures and tests utilized in
the examples, will be described.
Test Methods For the Uncuredpressure-Sensitive Adhesive Tapes
90.degree. Peel Adhesion
90.degree. C. peel adhesive was determined using PSTC-2, a
procedure specified in "Test Methods for Pressure Sensitive
Adhesive Tapes," 12th edition, available from the
Pressure-Sensitive Adhesive Tape Council, 401 North Michigan
Avenue, Chicago, Ill. 60611-4267, U.S.A.
A 1.27 cm.times.8 cm strip of an unsupported pressure-sensitive
adhesive tape (200 .mu.m thick) between two release layers was
prepared as described in Example 1 and allowed to age for at least
24 h before testing. One release liner was removed and the exposed
material pressed by hand onto the dull side of a 125 .mu.m thick
foil of anodized aluminum which serves as a backing for the tape
construction. The anodized aluminum foil was 1.6 cm wide.
The second release liner was removed and the exposed surface
adhered to a stainless steel test panel which had previously been
cleaned with methyl ethyl ketone and heptane. The construction thus
prepared was configured in such a manner that the anodized A1 foil
had an unbonded adhesive-free tab of about 10 cm for attachment to
a tensile tester. The bonded construction was then passed over
twice with a 6.8 kg roller and allowed to remain in contact with
the test substrate for about 20 minutes before testing.
The test construction thus obtained was then placed in a tensile
tester (Instron.TM.) so that the aluminum foil was peeled away from
the stainless steel test panel at an angle of 90 degrees. The peel
adhesion was measured at a speed of 30.5 cm per min. and was
recorded in N/1.27 cm.
The test was repeated 2 times and the results then averaged.
Holding Power
A modified version of PSTC-14 was applied, a procedure specified in
"Test Methods for Pressure Sensitive Adhesive Tapes," 12th edition,
available from the Pressure-Sensitive Adhesive Tape Council, 401
North Michigan Avenue, Chicago, Ill. 60611-4267, U.S.A.
An unsupported pressure-sensitive adhesive tape having a thickness
of approximately 200 microns, sandwiched between two siliconized
PET release liners, was cut in the form of a strip 1.27 cm wide and
8 cm long. One release liner was removed and the exposed adhesive
face bonded to a strip of anodized aluminum sheeting which was 125
microns thick, 1.6 cm wide and about 10 cm long in such a manner
that a 2 cm area on the end of the aluminum strip was not covered
with adhesive.
The second release liner was removed and the entire exposed
adhesive face adhered to a rigid aluminum plate which had been
cleaned twice with heptane. The assembly thus formed was then
passed over four times with a 2 kg roller.
After a dwell time of one minute, the assembly was suspended
perpendicular to the gravitational force direction by attaching one
end of the rigid aluminum plate to a vertical stand in such a way
that the rigid aluminum substrate was uppermost and the flexible
aluminum sheeting was suspended below it.
A 150 g weight was then attached to the exposed end of the aluminum
sheeting which was not bonded to the aluminum plate. The time
required for the adhesive bond to fail as measured by the falling
of the weight was recorded in minutes.
Static Shear
This test is based on PSTC Method PSTC-7 (Procedure A), a procedure
specified in "Test Methods for Pressure Sensitive Adhesive Tapes,"
12th edition, available from the Pressure-Sensitive Adhesive Tape
Council, 401 North Michigan Avenue, Chicago, Ill. 60611-4267,
U.S.A. All measurements of this type were made at room temperature.
An unsupported pressure-sensitive adhesive tape having a thickness
of approximately 200 .mu.m, sandwiched between two release liners
was obtained as is described in Example 1. One release liner was
removed and replaced by a 125 .mu.m thick layer of anodized
aluminum sheet. The second release liner was then removed, yielding
an adhesive tape with an aluminum backing which was used in the
static shear test. A 1.27 cm wide strip of tape prepared by the
method just described was adhered to a flat, rigid, stainless steel
plate with 2.54 cm length of tape in contact with the panel. The
total bonded area was then 1.27 cm.times.2.54 cm. Then the panel
with the adhered tape test sample was placed in a special stand
tilted at two degrees from vertical for 10 minutes. Then a weight
of 50 g was hung from the free end of the tape. The time required
for the weight to fall is the Static Shear Value in hours.
Test Methods For the Cured Pressure-Sensitive Adhesive Tapes
Impact Resistance
A modified version of ISO 9653 was applied. Modification consisted
of changes in the sample assembly configuration and bonded area. A
custom stage was built so that metal test plates sides could be
mechanically held in the stage area and smaller test bodies adhered
to them.
The configuration of the bonded assembly used for making the test
measurements comprised an aluminum test body having the dimension
of 15 mm.times.20 mm.times.5 mm adhered to an aluminum test plate
having the dimensions 2.54 cm.times.10 cm.times.2 mm. The test body
was located in relationship to the test plate so that the 10 cm
side of the test body was parallel to a line defining the minimum
point of the pendulum swing. The bonded area was 1.27 cm.times.2
cm. Both the aluminum test plate and the aluminum test body were
cleaned by light abrasion with a Scotchbrite.TM. scouring pad with
water and then washing with MEK, then isopropanol, followed by a
final rinse with MEK. The aluminum pieces were then allowed to air
dry before the test assembly was prepared.
A 250 micron thick unsupported pressure-sensitive adhesive tape
which was prepared as described in Example 1 and allowed to age for
at least 24 hours before testing. A sample having the dimension of
1.27 cm.times.2.0 cm was cut.
One liner was removed and the exposed pressure-sensitive adhesive
irradiated with 200 mJ/cm.sup.2 from a ultraviolet light bulb
(H-bulb available from Fusion Systems Corporation, Rockville, Md.,
USA) contained in a high intensity ultraviolet light source, also
commercially available from Fusion Systems Corporation. The amount
of energy used to irradiate the adhesive face was measured using a
UVI MAP (TM) UV and Temperature Measuring/Plotting System, Model
UM365H-S (Electronic Instrumentation Technology Inc., Starling,
Va., USA) designed to measure UV-A radiation in the range of
320-390 nm. The device was calibrated according to N.I.S.T.
standards (National Insitute of Standards and Technology). The
irradiated pressure-sensitive adhesive was then adhered to the
aluminum test body in such a manner that the 1.27 cm width of the
adhesive strip was centered and parallel to the 20 mm edge of the
test body.
The second liner was then removed from the adhesive and irradiated
in the same fashion as above. The exposed adhesive was then adhered
to test plate, thus bonding the test body and the test plate
together.
The bonded assembly was then clamped together with pliers using
moderate hand pressure for about one second. The bonded sample
assembly was allowed to cure at 23.degree. C. at 50% relative
humidity for three days before testing.
A commercially available impact tester, available as Model 5102
from Zwick GmbH, Ulm, Germany, was employed. A 4 Joule pendulum,
corresponding to a weight of 934.6 g was employed at a speed of
2.93 m/s. This speed was generated by raising the pendulum to the
full extension of 160.degree. on an arm length of 225 mm before the
weight was released and allowed to strike the sample assembly in a
shearing mode described in ISO 9653 and designed to shear the test
body off of the test plate.
The amount of energy absorbed by the sample assembly as the
pendulum broke the adhesive bond was measured by reading the height
of the pendulum swing and recorded in Joules. The test was
conducted on each of three separate assemblies and the results
averaged.
Overlap Shear
A modified version of ISO 4587 was employed.
Aluminum coupons (100 mm.times.25 mm.times.2 mm) were subjected to
light abrasion treatment with a Scotchbrite.TM. scrubbing pad
(available from 3M Company) followed by soap/water and finally
cleaned with isopropanol.
The assemblies were prepared by removing one of the two protective
liners from a pressure-sensitive adhesive strip (1.27 cm.times.2.54
cm ) as generated in the examples, irradiating the exposed adhesive
surface in the manner described in the test section for Impact
Resistance above except that the pressure-sensitive adhesive tape
was irradiated with 400 mJ/cm.sup.2 from both sides, and then
bonding the irradiated adhesive to the aluminum coupon. The second
protective liner was removed and the second surface of the adhesive
irradiated as well in the same manner. Finally the second surface
of the adhesive tape was bonded to the second aluminum coupon in a
configuration described in the standard method. The adhesive was
aligned with the longer side perpendicular to the direction of the
applied force during the test and it was always placed so that it
was flush with the end of the bonded coupon.
The bonded assemblies were clamped together with a pliers using
moderate hand pressure for approximately 1 second and allowed to
cure at 23.degree. C. and 50% relative humidity for at least three
days before testing.
Dynamic overlap shear test were performed on assemblies comprising
the sequence A1 coupon/adhesive/A1 coupon prepared as described
above. The test method deviated from the standard test method
specified above in that the crosshead speed was 5 mm/min. The test
was repeated three times for each sample and the average value was
recorded in Mpa.
Materials Used in the Examples
Polyester Compounds
DYNAPOL S 1313, amorphous copolyester, T.sub.g =13.degree. C.,
softening point T.sub.s =100.degree. C., commercially available
from Huls AG, Marl, Germany.
DYNAPOL S 1421, amorphous copolyester, T.sub.g =-4.degree. C.,
T.sub.s =80.degree. C., commercially available from Huls AG, Marl,
Germany
DYNAPOL S 1402, slightly crystalline copolyester, T.sub.g
=-12.degree. C., melting point T.sub.m ==92.degree. C.,
commercially available from Huls AG, Marl, Germany
DYNAPOL S 1359, slightly crystalline copolyester, T.sub.g
=-16.degree. C., T.sub.g =100.degree. C., commercially available
from Huls AG, Marl, Germany
DYNAPOL S 1227, moderately crystalline copolyester, T.sub.g
=13.degree. C., T.sub.m =118.degree. C., commercially available
from Huls AG, Marl, Germany
DYNAPOL S 1228, moderately crystalline polyester, T.sub.g
=-3.degree. C., T.sub.m =110.degree. C., commercially available
from Huls AG, Marl, Germany
Epoxy Resins
DER 331, epoxy equivalent weight ca. 187, liquid at room
temperature and atmospheric pressure, commercially available from
Dow Chemical Comp., Midland, Mich.
EPON 1001, epoxy equivalent weight ca. 515, solid at room
temperature and atmospheric pressure, commercially available from
Shell Chemical
Hydroxyl Functional Compounds
VORANOL 230-238, polyol adduct of glycol and propylene oxide having
a hydroxyl number of 38, molecular weight (number average) of 700,
liquid at room temperature and atmospheric pressure, commercially
available from Dow Chemical, Midland, Mich. (termed in the tables
below as V 230-238)
SIMULSOL BPHE, a difunctional bisphenol A based polyol, liquid at
room temperature and atmospheric pressure, molecular weight (number
average) of 315, commercially available from Seppic, Paris, France
(termed below as BPHE)
SIMULSOL BPRE, a difunctional bisphenol A based polyol, liquid at
room temperature and atmospheric pressure, molecular weight (number
average) of 755, commercially available from Seppic, Paris, France
(termed below as BPRE)
TONE 0305, a trifunctional polycaprolactam based polyol, liquid at
room temperature and atmospheric pressure, molecular weight (number
average) of 540, commercially available from Union Carbide (termed
below as T 0305)
TERETHANE 1000, a difunctional poly THF based polyol, liquid at
room temperature and atmospheric pressure, molecular weight (number
average) of 1000, commercially available from DuPont (termed below
as T 1000)
Cationic Photoinitiator
UVOX UVI 6974, triarylsulfonium complex salt, commercially
available from Union Carbide, Danbury, Conn.
EXAMPLES
Examples 1-12
The polyester component (i), the epoxy component (ii) and the
hydroxyl-functional component (iii) as specified in Table 1 were
combined in a closed glass container and placed in a forced air
oven for 2 hours at 150.degree. C. The resulting mixture was
stirred until a homogeneous mixture was obtained. The
photoinitiator component (iv) as specified in Table 1 was then
added and the mixture was again stirred until the photoinitiator
was dissolved.
The resulting liquid mixture was then poured between two
siliconized PET release liners previously threaded onto a heated
hot knife coater. The hot knife coater had a bed temperature of
100.degree. C. and the knife was pre-heated in an oven to
120.degree. C. before coating. Hot-knife coating resulted in an
unsupported pressure-sensitive adhesive tape with a thickness of
about 200 .mu.m between the PET release liners.
The unsupported pressure-sensitive adhesive tapes were tested
according to the test methods specified above, and the results
obtained are summarized in Table 2.
Comparative Example 1
An unsupported pressure-sensitive adhesive film having the
composition specified in Table 1, was prepared according to the
method of Example 1. Although comprising the amorphous polyester
DYNAPOL S 1421, the unsupported pressure-sensitive adhesive film
exhibits a holding power of virtually 0 min. (see Table 2) which is
due to the high ratio of liquid/solid epoxy resins of about
1.93.
Comparative Example 2
An unsupported pressure-sensitive adhesive film having the
composition specified in Table 1, was prepared according to the
method of Example 1. Although comprising the amorphous polyester
DYNAPOL S 1313, the unsupported pressure-sensitive adhesive film
exhibits a holding power of less than 5 minutes (see Table 2)
because the ratio m.sub.(ii)+(iii) /m.sub.(i) is 1.75 which is too
high to give the required elasticity of the pressure-sensitive
adhesive tape.
Comparative Example 3
An unsupported pressure-sensitive adhesive film having the
composition specified in Table 1, was prepared according to the
method of Example 1. Although comprising the amorphous polyester
DYNAPOL S 1313, the unsupported pressure-sensitive adhesive film
exhibits a holding power of virtually 0 min. (see Table 2) which
results from the low ratio m.sub.L /m.sub.S of 0.
Comparative Examples 4-18
Unsupported pressure-sensitive adhesive films having the
composition specified in Table 1, were prepared according to the
method of Example 1. The films were tested according to the test
methods specified above, and the results obtained are summarized in
Table 2. The adhesive films of Comparative Examples 2-16 which
comprise slightly crystalline and moderately crystalline polymers,
exhibit insufficient values of the holding power.
TABLE 1 Polyester Hydroxyl- component Epoxy component functional
Photoinitiator DYNAPOL #, DER EPON component component amount 331
1001 Compound, UVOX UVI Ex. (wt. %) (wt. %) (wt. %) amount (wt. %)
6974 1 S 1313, 40 20 24 V230-238, 15 1 2 S 1313, 40 25 19 V230-238,
15 1 3 S 1421, 40 15 29 V230-238, 15 1 4 S 1421, 40 0 44 V230-238,
15 1 5 S 1313, 42.1 15.8 30.5 V230-238, 10.5 1 6 S 1313, 42.8 12.0
29.1 V230-238, 15.1 1 7 S 1313, 71.4 26.8 0 0 1.8 8 S 1313, 40 15
29 BPHE, 15 1 9 S 1313, 40 15 29 BPRE, 15 1 10 S 1313, 40 15 29
T0305, 15 1 11 S 1313, 40 15 29 T1000, 15 1 C1 S 1421, 40 29 15
V230-238, 15 1 C2 S-1313, 36 16.9 32.6 V230-238, 13.5 1 C3 S-1313,
57.1 0 41.4 0 1.5 C4 S 1402, 40 29 15 V230-238, 15 1 C5 S 1402, 40
15 29 V230-238, 15 1 C6 S 1402, 40 0 44 V230-238, 15 1 C7 S 1359,
40 44 0 V230-238, 15 1 C8 S 1359, 40 29 15 V230-238, 15 1 C9 S
1359, 40 15 29 V230-238, 15 1 C10 S 1359, 40 0 44 V230-238, 15 1
C11 S 1227, 40 44 0 V230-238, 15 1 C12 S 1227, 40 29 15 V230-238,
15 1 C13 S 1227, 40 15 29 V230-238, 15 1 C14 S 1227, 40 0 44
V230-238, 15 1 C15 S 1229, 40 44 0 V230-238, 15 1 C16 S 1229, 40 29
15 V230-238, 15 1 C17 S 1229, 40 15 29 V230-238, 15 1 C18 S 1229,
40 0 44 V230-238, 15 1
TABLE 2 Holding Static 90.degree. Peel Impact Overlap power shear
adhesion resistance shear Ex. (min.) (hr) (N/1.27 cm) (kJ/m.sup.2)
(MPa) 1 21.1 >8 8.7 9.4 14.0 2 22.0 6.2 4.0 9.7 13.5 3 28.1 1.1
13.7 14.7 11.6 4 <30 8.9 29.6 9.8 9.0 5 >10 N/T 17.8 2.2 13.2
6 >10 N/T 8.7 N/T 7.1 7 >50 N/T 9.2 N/T 4.0 8 >10 N/T 33.8
0.7 N/T 9 >50 N/T 15.1 6.1 4.7 10 >10 N/T 18.7 3.8 6.6 11
>50 N/T 2.8 3.2 7.4 C1 N/A 0 2.0 14.0 13.2 C2 <5 N/T N/T N/T
N/T C3 N/A N/T 0 0 0 C4 N/A 1.9 1.4 N/A N/A C5 1.1 20.9 2.2 11.0
12.2 C6 2.2 >70 20.2 5.8 10.1 C7 N/A 0.2 N/A N/A N/A C8 N/A N/A
N/A N/A N/A C9 0.2 N/A 1.5 11.0 13.0 C10 0.7 0 18.4 7.5 11.2 C11
N/A N/A N/A N/A N/A C12 N/A N/A <0.5 0.5 <1 C13 N/A N/A 0.89
0.9 2.9 C14 N/A N/A 13.96 13.9 <1 C15 N/A N/A N/A N/A N/A C16
N/A N/A 0.75 0.8 13.3 C17 N/A N/A 2.16 2.2 <1 C18 N/A N/A 4.95
5.0 2.8 N/A: Not applicable. The test could not be conducted
because the materials had too little cohesive strength to be
handled, holding power virtually 0 min, and/or no proper sample
could be obtained for the respective test. N/T: Not tested.
* * * * *